Add configuration file for probot-stale - https://github.com/probot/stale

[amedyne]

Pull Request checklist

• Tests: This PR includes thorough tests or an explanation of why it does not
• Screenshots: This PR includes screenshots or GIFs of the changes made or an explanation of why it does not
• Accessibility: The code in this PR follows accessibility best practices or does not include any user facing features. In addition, it includes a screenshot of a successful accessibility scan to ensure no new defects are added to the product.

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[jonalmeida]

I ran this file through a YAML validator and found some small nits to fix, everything else looks good to me! 🙂